Servomotor mechanism



H- M. PURCELL SERVOMOTOR MECHANISM Filed Feb. 15, 1946 lNVENTOR HUWARD M. PURGELL 7W4.- W- ,y MM

' AT TORNEYS June 7, 1949.

Patented June 1, 1949 SERVOMOTOR MECHANISM Howard M. Purcell, Mount Gilead, Ohio, assignor to H-P-M Development Corporation, Wilming ton, Del., a corporation of Delaware Application This invention relates to hydraulic machinery, and, in particular, to control mechanism for hydraulic pumps of the variable delivery type.

Pumps of this type which may be of various constructions, for instance of the construction shown in U. 5. Patent No. 2,250,705 to Walter Ernst, are provided with a control member movable into various positions for varying the delivery f the pump. Such a control member has generally associated therewith a control mechanism which in response to a predetermined pressure in the hydraulic system, of which the pump forms a part, will automatically shift the control member into a position for causing the pump approximately to stop delivery of fluid.

These pumps have been quite satisfactory in ordinary hydraulic circuits. However, where it is desired, as for instance in hydraulic circuits for drawing presses, to maintain a certain dwell, i. e., to hold vthe drawing-pressure for a certain period February 15, 1946, Serial No. 647,786

4 Claims. (Cl. 121 -41) easily be adjustable to vary the pressure for actuation of the control member.

These and other objects and advantages of the invention will appear more clearly from the fol-,- lowing specification in connection with the accompanying drawing in which:

Figure l is a section through the control mechanism according to the invention.

Figure 2 illustrates a hydraulic circuit comprising a variable delivery pump with the control mechanism illustrated in Figure 1;

General arrangement In general, the arrangement according to the present invention comprises a casing housing a spring which engages a part of a valve member adapted to control the delivery of pilot fluid to I the servomotor for the variable delivery pump.

of time, the control mechanism for variable dej livery pumps as heretofore known havenot been able to meet the necessary requirements. The

reason for this failure consists in that the 'hy-' draulically operated control mechanismdid not stop the control rod in the position in which the pump does not deliver any fluid of only so much as it is necessary to-make up for leakage. Instead, the control rod moved beyondthis position, and as a result thereof, fluid was transferred from one side of the control member to the other side thereof and back so that a fluctuation of the control rod back and forth took place in order to sense the correct neutral position.

It is, therefore, an objectof the invention to provide a control mechanism for use in connection with variable delivery pumps which will overcome the above mentioned drawback.

It is another object to provide a control mech anism for variable delivery pumps which can easily be adjusted so as to definitely limit the stroke of the control rod when the latter shifts.

the pump into substantially no delivery position for holding a predetermined pressure.

It is a flirther object of the invention to provide a variable delivery pump with a control mechanism which will automatically reduce the delivery of the pump to substantially zero in response to a predetermined pressure at the delivery side of the pump, while preventing any fluctuation of the control member of the pump.

It is also an objector the invention to provide a control mechanism of the above mentioned type which will be simple in construction and will The casing housing this spring comprises an abutment which will be engaged by the valve member and will stop the movement of thelatter when the valve member is actuated in response to a predetermined pressure governing the movement of the pump to substantially no delivery position. To vary'the pressure at which this shifting movement of the pump is to be effected, the casing housing the spring is provided with adjusting means for adjusting the tension of the spring.

Structural arrangement Referring now to the drawing and Figure 1 thereof in particular, this figure shows a part of the pump casing to of a variable delivery pump. Connected to the pump casing I0 is a cylinder ll having a bore l2 and a larger bore IS in which a piston I4 is reciprocably mounted. The piston It has a radial bore l5 and a horizontal bore l6 which latter is adapted to efiect communication between the recess I! in the larger portion Ma of the piston and the annular recess H3 in the smaller portion Nb of the piston it. The radial bore l5 communicates with an annular recess IS in the piston portion Mb. The piston M has connected thereto a sleeve '20 provided with radial bores 2| and 22 respectively in alignment with the bore l5 and the annular recess I8. The piston I4 is adapted to be engaged by a split ring 23 which in its turn engages an annular groove 24 of the servomotor Slidably mounted in the bore 21 is the plunger 28 then extends through packing 34 located inthe lid 35a which latter is connected to the cylinder II in any convenient manner. The

left end of the plunger 28 with regard to Figure 1 extends into a cylinder 35 having a bore 85 and a larger bore 81. Reciprocably mounted in the bore 31 is a piston 38 which is clamped against the step 88 of the plunger 28 by means of a nut 48 which latter is screwed upon the end of the plunger 28 and secured thereto by a threaded pin 4|.

shifted to the left with regard to the drawings. .As a result thereof the cylinder 85, together with the casing 46 and the plunger 28 as a unit move toward the right. Consequently, fluid connection is now stopped between the conduit H, a bore l5 and 2| and recess I 1. Therefore, provided that the pilot pump 18 has been started. pressure fluid will be supplied by the pilot pump 18 to the left hand side of the piston area Ida of the piston l4. As a result thereof, the piston '14 will move toward the right and, will shift the servomotor rod 25 accordingly so as to place the pump I8 on forward stroke. The pump I8 will then deliver pressure fluid through conduit The nut 48 is engaged by one end of a spring 42, the other end of which abuts a disc 43 movable in the bore 45 of the casing 45. The casing 45 is screwed into the cylinder 35 and is held in position with regard thereto by a locking nut 41. The disc 48 is adjustably engaged by an ad- Justing screw 48 which latter is covered against outside interference by an acorn nut 48. The device is furthermore provided with seals 58, 5| and 52 to prevent leakage. Furthermore, the plunger 28 has a longitudinal bore 53 therein which communicates with radial bores 54 and 55 for conducting drainage.

Linked to the cylinder 85 is a link 56 which in its turn is connected to the lid a by a link 51.

- The device shown in Figure 1 may be ar-j ranged in a hydraulic circuit such as the circuit 7 shown in Figure 2. This circuit shows one side 58 to the hydraulic motor 88, while the exhaust from the motor 88 will be returned through conduit8l tothepump l8.

When during the operation of the motor 88 a predetermined pressure for which the spring 42 has been set has been built up in the motor 68, this pressure will be'conveyed through conduits 58 and 14 to the bore 81 where it will act on both the step 88 and the piston 88. Inasmuch as the area of the piston 88 is the larger one, the pressure acting thereupon will move the piston 38 and through nut 48 also the plunger 28 toward the right until the nut 48 abuts the adjacent end of the casing 45. When this position has been reached, pressure fluid from the pump I8 will be conveyed through conduit H and bore I5 to the right side of the piston portion l4a while fluid connection is interrupted between the conduit H and the left side area of the piston portion I la. Consequently, the pressure fluid acting on the right hand side of the piston portion l4a will move the piston l4 leftwardly until the relative position between the piston .l4 and the plunger 281s that shown-in Figure 1. During this leftward movement of the piston portion |4a the fluid expelled from the recess ll will pass through bore I6,- annular recess I 8 and bore 32 as well as the radial bores 25 into the exhaust conduit'il from where it will be returned to the fluid reservoir or I8 is provided with centering springs 82 and 53 i adapted to actuate the shift ring or flow control member 64 by means'of the centering rod 85, for shifting the pump l8 into neutral or no delivery position in case of a failure of power to thereby prevent accidents. This centering arrangement does not form a part of the present invention and is more fully described in U. S. Patent No. 2,184,665 to Walter Ernst. Also connected to the shift ring 54 is the servomotor rod 25.

The cylinder bore l2 in the cylinder II is connected by means'of a bore 58 with a conduit 51 leading to a fluid reservoir or tank 68. Also connected to the tank 58 is a conduit 88 leading to the suction side of a pilot pump 18 which may be of any desired type. The pressure side of the pump I8 communicates through a conduit H with a bore 12 in the cylinder II. Interposed between the suction and pressure side of the pump 18 and communicating with the conduits 88 and H is the pressure relief valve 13 of any standard construction. The conduit 58'further communicates through a flexible conduit" 'with" the bore 15 leading into the bore' 31 I Operation It may be assumed that all parts of the hytank 68. During this leftward movement of the piston I 4, the servomotor rod 25 will likewise be moved leftwardly in such a manner that when piston l4 comes to rest the shift ring of the pump l8, and consequently also the pump I8, is in substantially no delivery position; Since the plunge'r 28 is definitely arrested-due to the abutment of the nut 48 against the casing, no hunting of the plunger 28 can take place, and the pump |8will stay in neutral position, thereby maintaining its pressure holding position constant until by movement of the lever 56 it is desired to place the pump I8 in the reverse stroke.

To this end the lever-56 is shifted to the rightwith regard to Figure 1, thereby also shifting the plunger 28 toward the right. This will again space the nut 48 from the casing 46, while simultaneously establishing again fluidconnection between conduit H andthe right hand area of the piston portion Ha. Consequently, pressure fluid from the pilot pump I8 willcause the piston l4 to move further leftwardly, thereby placing the pump 18 on return stroke. Pressure fluid from the pump I 8 will then be conveyed through.

conduit 8| .to motor 68 and operate the same in the reverse direction. The pump l8 may be stopped at any time during the operation of the motor 68 by shifting the lever 58 leftwardly with regard to Figure 1 so that pressure fluid will be conveyed from conduit H to the leftward area of the piston portion I441. The fluid pressure will then move the piston toward the right until a said valve may be shifted independently relative position has been obtained as shown in Figure 1. In this position, the piston l4 comes to a stop while the pump I0 is in substantially no delay position.

It may be noted that the plunger portions 28 and 30 have the same diameter so that they are hydraulically balanced and that no drainage which may enter the space between the said two plunger portions will in any way affect the position of the plunger 29.

If it is desired to vary the pressure at which the pump it should move into substantially no delivery position, it is merely necessary to unscrew the acorn nut 49 and adjust the adjusting screw 48 to the desired extent.

It will be understood that the present invention is by no means limited to the particular construction shown in the drawing but comprises any modifications within the scope of the appended claims.

Having thus fully described my invention, what I claim as new and desire'to secure by Letters Patent, is:

1. In a servomotor, a casing, a double acting ram in said casing, a valve in said ram for controlling the supply of fluid to and from opposite ends of said casing, a rod on said valve having a piston, a cylinder on said rod surrounding said piston, resilient means in said cylinder urging said piston toward one end thereof, means to admit pressure to said one end of said cylinder to urge said piston toward the other end thereof, and mechanism linked to said cylinder for normally actuating said cylinder, rod and valve as a unit and for holding said cylinder stationary when said piston is actuated by pressure whereby of said mechanism and cylinder.

2. In a servomotor, a reciprocable ram, a valve for controlling the supply of fluid to and from opposite ends of said ram, a projection on said valve having a piston, cylinder means receiving said piston, resilient means in said cylinder urging said piston toward one end thereof, means to admit pressure between the said one end of said cylinder and said piston for urging the latter toward the other end of said cylinder, adjustable abutments in said cylinder to halt said piston in a predetermined position in its travel toward said other end, and mechanism linked to said cylinder for normally actuating said cylinder and piston as a unit and for holding said cylinder stationary when said piston is actuated by pres- 1 sure whereby said valve may be shifted independently of said mechanism and cylinder.

3. In a servomotor; a casing having a fluid inlet port, a double acting ram reciprocable in said casing and formed with an axial bore and a radial passage in communication with the fluid inlet port of said casing and the bore of said ram; a valve member slidably carried within the bore of said ram for controlling the passage of fluid introduced within said casing by way of the fluid inlet port to and from opposite ends of said casing; a rod extending longitudinally outwardly from said valve member and having a piston at one end thereof; a cylinder surrounding said piston; spring means in said cylinder urging said piston toward one end thereof; a fluid inlet port at said one end of said cylinder for admitting fluid thereto to urge said piston toward the 0pposite end of said cylinder; and lever means linked to said cylinder for normally actuating said cylinder, said rod and said valve member as a unit and for holding said cylinder stationary during actuation of said piston by pressure fluid introduced within said cylinder by way of said lastnamed fluid inlet port, whereby said valve member may be shifted independently of said lever means. 4. In a servomotor; a. reciprocable ram; a valve for selectively directing a supply of fluid to and from opposite ends of said ram; a rod extending from said valve and having a piston; a cylinder slidably receiving said piston; spring means in said cylinder urging said piston toward one end of said cylinder; a fluid inlet in said cylinder for admitting pressure fluid between the said one end of said cylinder and said piston for moving the latter toward the other end of said cylinder; adjustable abutments in said cylinder to halt said piston in a predetermined position in its travel toward said other end of said cylinder; and lever means linked to said cylinder for normally actuating said cylinder, piston and rod as a unit and for holding said cylinder stationary when said piston is actuated by pressure fluid, whereby said valve may be shifted independently of said lever means.

HOWARD M. PURCELL.

REFERENCES crrED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,628,603 Ferris May 10, 1927 1,679,544 Robson Aug. '7, 1928 1,814,565 Lombard July 14, 1931 1,861,116 Ernst May 31, 1932 1,870,501 Ernst Aug. 9, 1932 2,214,552 Ferris Sept. 10, 1940 2,258,981 Ernst Oct. 14, 1941 2,346,254 Ernst Apr. 11, 1944 

